What is a Task Queue?

Task queues are used as a mechanism to distribute work across threads or
machines.

A task queue’s input is a unit of work, called a task, dedicated worker
processes then constantly monitor the queue for new work to perform.

Celery communicates via messages using a broker
to mediate between clients and workers. To initiate a task a client puts a
message on the queue, the broker then delivers the message to a worker.

A Celery system can consist of multiple workers and brokers, giving way
to high availability and horizontal scaling.

Celery is written in Python, but the protocol can be implemented in any
language. So far there’s RCelery for the Ruby programming language, and a
PHP client, but language interoperability can also be achieved
by using webhooks.

What do I need?

Celery version 3.0 runs on,

Python (2.5, 2.6, 2.7, 3.2, 3.3)

PyPy (1.8, 1.9)

Jython (2.5, 2.7).

This is the last version to support Python 2.5,
and from Celery 3.1, Python 2.6 or later is required.
The last version to support Python 2.4 was Celery series 2.2.

Celery requires a message broker to send and receive messages.
The RabbitMQ, Redis and MongoDB broker transports are feature complete,
but there’s also support for a myriad of other solutions, including
using SQLite for local development.

Celery can run on a single machine, on multiple machines, or even
across datacenters.

Get Started

If this is the first time you’re trying to use Celery, or you are
new to Celery 3.0 coming from previous versions then you should read our
getting started tutorials:

Workers and clients will automatically retry in the event
of connection loss or failure, and some brokers support
HA in way of Master/Master or Master/Slave replication.

Fast

A single Celery process can process millions of tasks a minute,
with sub-millisecond round-trip latency (using RabbitMQ,
py-librabbitmq, and optimized settings).

Flexible

Almost every part of Celery can be extended or used on its own,
Custom pool implementations, serializers, compression schemes, logging,
schedulers, consumers, producers, autoscalers, broker transports and much more.